1. Field of the Invention
The present invention relates to an ink jet recording apparatus which performs recording on a recording medium.
2. Description of the Related Art
Recently, in order to meet market demands for higher image quality and higher speed of recording in an ink jet recording apparatus, the realization of multiple colors, higher density, smaller drops, a larger number of nozzles, and the like are progressing. As a result, the ink jet recording apparatus is able to provide a user with a photo image which is no way inferior to a silver halide photograph when printing to special media as well as for the purposes of printing of web content or a text on a plain paper. Additionally, an ink jet recording apparatus for business or industry with increased printing speeds like those of a laser beam printer has also been developed.
In the ink jet recording apparatus for business or industry, the nozzles of the recording head are often made long in order to increase the printing speed. However, in such an ink jet recording apparatus, it is difficult to keep constant the distance (hereinafter referred to as the “distance with respect to sheet”) from the nozzle face of a recording head to the recording face of the recording medium. This is because the distance from a pinch roller which supports the recording medium on the upstream side from the recording head to a sheet ejection roller which supports the recording medium on the downstream side from the recording head becomes longer. In such an ink jet recording apparatus, floating of a recording medium, a flapping (cockling) phenomenon which is caused as ink permeates into a recording medium, or the like easily occurs, it is difficult to keep the distance with respect to sheet constant between the pinch roller and the sheet ejection roller.
In the ink jet recording apparatus, in order to keep the distance with respect to sheet constant, an electrostatic adsorption conveyance system, a perforated platen conveyance system, or the like is used. The electrostatic adsorption conveyance system adopts an endless conveying belt in a recording medium conveying mechanism, and makes static electricity generated on the surface of the conveying belt adsorb and convey the recording medium. The perforated platen conveyance system makes the back of a recording medium be air-adsorbed on the conveying belt immediately below a recording area.
In Japanese Patent Application Laid-Open No. 2001-353861, an ink jet recording apparatus including an electrostatic adsorption conveyance system is disclosed. The electrostatic adsorption conveyance system of this ink jet recording apparatus performs DC (Direct Current) charging on a conveying belt with a high-resistance single layer structure, and adsorbs and conveys a recording medium.
Also in Japanese Patent No. 3804928 and Japanese Patent Application Laid-Open No. 2004-262557, an ink jet recording apparatus including an electrostatic adsorption conveyance system is disclosed. The electrostatic adsorption conveyance system of these ink jet recording apparatuses performs AC (Alternating Current) charging on a conveying belt with a two-layer structure in which the surface layer is an insulating layer and the back layer is a conductive layer, and adsorbs and conveys a recording medium.
In the electrostatic adsorption conveyance system, which performs DC charging on the conveying belt of a single layer structure, disclosed in Japanese Patent Application Laid-Open No. 2001-353861, it is known that an abrupt decrease in the adsorption force of the conveying belt to a recording medium may occur when the recording medium is adsorbed and conveyed. Thereby, deterioration of image quality due to floating of the recording medium or rubbing of the surface of the recording medium caused by the interference between the recording medium and the recording head may occur.
Additionally, it is known that, if the charging method is changed to the AC charging from the DC charging in the configuration of the electrostatic adsorption conveyance system disclosed in Japanese Patent Application Laid-Open No. 2001-353861, the abrupt decrease of the adsorption force of the conveying belt to the recording medium becomes rather conspicuous.
In the electrostatic adsorption conveyance system, which performs the AC charging on the conveying belt of a two-layer structure, disclosed in Japanese Patent No. 3804928 and Japanese Patent Application Laid-Open No. 2004-262557, a recording streak may be confirmed at the timing (pitch of half of a positive or negative charging cycle) with which positive and negative charges applied to the conveying belt are switched.
Although the average charging distribution of the conveying belt immediately below the recording head is uniform since the surface potential becomes “0”, a positively charged portion and a negatively charged portion are microscopically generated in the conveying direction of a recording media on the conveying belt. On the boundary portion between the positively charged portion and the negatively charged portion, an ink drop discharged onto a recording medium is pulled toward the positively charged portion or the negatively charged portion by Coulomb forces. Therefore, since the ink drop does not land exactly on the recording medium at the boundary portion between the positively charged portion and the negatively charged portion on the conveying belt, it is believed that this appears as a recording streak. This phenomenon is particularly conspicuous in a case where the velocity of an ink drop is slow.
Moreover, in a case where the AC charges are imparted to the conveying belt, it is known that there is also a problem in that the adsorption force of the conveying belt to the recording medium decreases abruptly when ink mist or dust adheres to the conveying belt. In a case where positively charged portions and negatively charged portions are repeatedly formed in the conveying direction on the conveying belt which has been subjected to the AC charging, and the surface resistance of the conveying belt is high, movement of charges does not occur between the positively charged portion and the negatively charged portion. However, since the surface resistance of the conveying belt decreases in a case where ink mist, dust, or the like adheres to the conveying belt, movement of charges occurs between the positively charged portion and the negatively charged portion of the conveying belt. Thereby, since the surface charges of the conveying belt will be cancelled, it is believed that the adsorption force of the conveying belt to the recording medium will decrease.